You could argue any link is a good link, excluding, obviously, links from spammy websites. But there are various levels of goodness across links.

A reciprocal link is good for a new site seeking to be found early in their lifecycle. You gotta start somewhere, and in addition to potentially being a discovery point for a new site, that link could send direct traffic to the new site from the more established website. These links don’t hold a lot of value for organic ranking per se, but in reality, you need to build your site for more than just pleasing the engines.

A direct link inside the content of the page is really what you want. These types of links usually happen because someone is talking about either you, or the topic you're related to. In many cases, this is positive and we see those signals as being beneficial to you.

Site wide links often happen, and while they can be beneficial in terms of maybe driving direct traffic to your site, they are much less useful for organic ranking. A site wide link is less of an endorsement than being mentioned in the body copy of the page. Plus, site wide links may often see links to you from pages of content unrelated to your own content.

Links in press releases can provide some value, but by their very nature, press releases are self-promotional, which kind of defeats the whole idea behind organic links. Just because the press release is hosted by someone else doesn't meant we won't understand the self-promotional nature of the link. Now, if the release is picked up by a news service, and a story is posted on their site, the link from them to you could be helpful, but there are limits...

This last group we'll call relational links. While a link from CNN could drive a ton of traffic your way, its value to organic rankings is somewhat muted. You see, CNN is in the news business. For this example, we'll say you're in the heli-skiing business. See how they are not really related? Now, a link from a major manufacturer of skiing products, that would have value in helping your rankings.